Resonator

RESONATOR, a body or system in which oscillations arise due to resonance (see). One can speak of mechanical, acoustic, and electrical resonators, depending on the nature of the arising oscillations. In acoustics, the greatest importance is represented by the air resonator, i.e., a bounded volume of air that comes into oscillation under the influence of sound waves reaching it and thus amplifies sounds of a definite pitch. A pipe closed at one end resonates to sound waves when the geometrical length of the pipe is ¹/₄ of the wavelength of the incoming sound wave. Sound analysis can be produced with the help of a set of resonators. For this purpose, air resonators are used in the form of hollow spheres (Helmholtz resonator) or cylinders, which have an opening at one end for incoming sound waves and an appendage at the other with an opening for connecting the resonator to the ear. The proper tone of a resonator is higher the smaller the volume of air enclosed within it. König used a resonator representing sliding cylinders fitting tightly one into another; such a resonator changes the pitch of its proper tone when its length is changed. Besides this, the pitch of a resonator depends on the size of the opening through which the sound waves enter. According to the empirical formula of Sondhaus, the natural frequency of oscillation of a resonator f = 5240 √s/V, where s is the area of the opening (cm²) and V is the volume of the resonator (cm³). To determine which tones are part of a complex sound, different resonators of the set are applied to the ear alternately; the amplification of sound by certain resonators indicates the presence of corresponding tones in the complex sound. In the vocal apparatus, air resonance is provided by the oral and nasal cavities, which amplify certain tones arising during the passage of an air stream through the vocal cords. The different arrangement of these cavities accounts for the amplification of greater or lesser high overtones in the produced sound, due to which various vowel sounds are created. Using cylindrical air resonators in front of whose openings corresponding tuning forks were placed, Helmholtz produced the synthesis of various vowels, thereby proving that vowel sounds of speech are caused by overtones entering into the composition of the complex sound and lying in a definite frequency range. The resonators in the auditory apparatus are the fibers of the basilar membrane (membrana basilaris)—see Resonance. Stringed musical instruments are provided with resonators—soundboards—which are flat (piano, zither) or of complex shapes (violin, cello). These resonators are characterized by strong damping of oscillations, which is why they resonate to a wide frequency range.